This invention relates to a chiral bisphosphine-rhodium complex. More specifically, this invention relates to a chiral bisphosphine-rhodium complex as a catalyst for the asymmetric reduction of a tetramisole precursor which allows the synthesis of levamisole in high optical yield.
The use of bisphosphine-rhodium complexes as a catalyst is disclosed as follows:
U.S. Pat. No. 3,949,000 discloses asymmetric diphosphines which, when reacted with a rhodium-halogen salt, produce rhodium complexes. The rhodium complexes are then used as catalysts for the hydrogenation of precursors of amino acids.
Canadian Pat. No. 977,373 discloses rhodium coordination complexes, containing a phosphine and at least one halogen ion, wherein the optical activity of the complex resides in the phosphine ligand. These complexes are useful as catalysts in the asymmetric hydrogenation of precursors of .alpha.-amino acids.
Asymmetric Catalysis by Chiral Rhodium Complexes in Hydrogenation and Hydrosilylation Reactions, H. B. Kagan, "Pure and Applied Chemistry," 43, p. 402 (1976) discloses asymmetric catalytic reduction of optically active enamides and precursors of .alpha.-amino acids using a chiral diphosphine rhodium complex as a homogeneous catalyst.
All of the above references are incorporated herein by reference.
Also, U.S. Patent Application Ser. No. 739,923 filed Nov. 8, 1976, now U.S. Pat. No. 4,087,611 which is a CIP of U.S. Patent Application Ser. No. 680,302, filed Apr. 26, 1976 now abandoned, discloses a process of using a chiral rhodium-diphosphine catalyst to directly manufacture an optically active levamisole. See, e.g. U.S. Patent Application Ser. No. 739,923, page 9.
The utility of the compound of this invention: chiral-2,3-Bis(diphenylphosphinomethyl)bicyclo[2.2.1]heptane is as an intermediate in the manufacture of a chiral rhodium-diphosphine catalyst which is useful in the reduction of a tetramisole precursor to give a significant excess of the desired S-(-) isomer, levamisole. The chiral rhodium-diphosphine catalyst and the process of using the catalyst in the reduction of the tetramisole precursor is also novel.